Marinate the Beef: Slice the beef thinly against the grain to ensure tenderness. In a bowl, combine the beef with soy sauce, oyster sauce, cornstarch, sesame oil, and black pepper. Mix well and let marinate for 15–20 minutes.
Prepare the Black Pepper Sauce: In a small bowl, whisk together oyster sauce, soy sauce, dark soy sauce, brown sugar, cracked black pepper, beef broth, and cornstarch until smooth. Set aside.
Sear the Beef: Heat 1 tablespoon of vegetable oil in a large wok or skillet over medium-high to high heat. Add the marinated beef in a single layer, working in batches if necessary. Sear for 1–2 minutes per side until browned. Remove from the pan and set aside.
Stir-Fry the Vegetables: Add the remaining tablespoon of oil to the same pan. Add the sliced onions, red bell peppers, and green bell peppers. Stir-fry for 2–3 minutes until slightly softened but still crisp. Add the garlic and ginger, cooking for another 30 seconds until fragrant.
Combine Everything: Return the beef and any accumulated juices to the pan. Stir the prepared black pepper sauce again, then pour it over the beef and vegetables. Toss everything together until evenly coated.
Simmer Until Glossy: Cook for another 1–2 minutes, stirring continuously, until the sauce thickens into a rich, glossy coating and the beef is cooked through. Avoid overcooking to keep the beef tender.
Serve and Enjoy: Transfer the tender black pepper beef to a serving plate. Sprinkle with extra freshly cracked black pepper if desired. Serve hot with steamed white rice.
Notes
For extra flavor, let the beef marinate longer if time allows.
Adjust the amount of black pepper according to your spice preference.
Serve with steamed vegetables for a complete meal.